Automatic circuit breaker



NOV. 12, 1935. J SACHS 2,020,330

AUTOMATIC CIRCUI-T BREAKER Filed Sept. 22, 1955 W I I Inn E aa l m is! i;

[Ml/527602" d0 sap/7 555/75 y titarngy Patented Nov. 12, 1935 UNITED STATES- PATENT OFFICE This inventionrelates particularly to an automatic circuit breaker of the type set forth in my Patents Nos. 1,811,970, 1,812,842 and 1,812,843, all

dated June 30, 1931 and in my reissued Patent 5 No. 18,894 dated July 11, 1933.

' In certain of the before-mentioned prior patents I have disclosed insulating walls associated with the circuit breaker contacts and so arranged as to lie adjacent the path of movement of the i movable contact and to thus partly confine any gases that may be formed as the result of arcing when the contacts are separated. In none of the prior constructions, however, is the path of movement of the movable contact, completely surrounded, and in each instance there is an unobstructed opening or space at least at one side which permits uncontrolled expansion of the arcfirmed gases, at least to a limited extent. While the prior constructions are effective to greatly 20 minimize the deleterious eflects of arc-formed gases, they do not completely surround the arcing zone and do not completely control the said gases. One object of the present invention is to provide, in association with the circuit breaker contacts, insulating means having walls which are so positioned as to substantially completely surround the path of movement of each movable contact and which thus substantially completely control and more effectively cool arc-formed 30 gases and shield the other parts of the circuit breaker from such gases.

Another object of the invention is to provide, in a circuit breaker of the type referred to, an insulating barrier at the outer side of the movable electroresponsive means. When this means is a bi-metallic thermal latch the barrier extends substantially from one end to the other thereof. This barrier serves to mechanically protect the electro-responsive means and to assist in excluding arc-formed gases therefrom.

A further'object of the invention is to provide certain details of construction for the movable contact carrying member which make it possible for the said member to be conveniently molded, instead of being formed of spaced fiat plates as in the earlier constructions referred to.

A still further object of the invention is to provide, in a circuit breaker of the type referred to, 50 a readily removable unit which comprises, in

combination, the two movable contacts and the bi-metallic thermal latch which connects them. Inasmuch as this combined unit is readily detachable, it is possible for it to be easily replaced 5 at any time, eitbel' t9 repair damage or to change the electrical characteristics of the circuit breaker.

In the accompanying drawing I have shown the embodiment of the invention which now seems preferable, but it will, be understood that 5 the drawing is intended for illustrative purposes only and is not to be construed as defining or limiting the scope of the invention, the claims forming a part of this specification being relied upon for that purpose.

Of the drawing:

Fig. 1 is a front view of the circuit breaker embodying ,the invention, certain of the conductin parts being shown in dotted lines.

Fig. 2 is a view similar to Fig. 1 with the front cover removed.

Fig. 3 is a vertical sectional viewtaken along the line 3-4-of Fig. 2, the circuit breaker being in open position.

Fig. 4 is a vertical sectional view taken along the line H of Fig. 2, the circuit breaker be in closed position.

Fig. 5 is a transverse sectional view taken along the line H of Fig. 3.

Fig. 6 is a detail perspective view showing the two molded parts of the contact member and also showing the removable unit consisting of the two movable contacts and the bi-metallic thermal latch.

Referring to the drawing, I represents the main insulatingbase or support which carries all of the other parts of the circuit breaker. Fitting the base I, at the front thereof is an insulating cover 2. Carried by the base I at the front thereof and within the cover are two simi- 35, lar substantially stationary main contacts 3 and l which are connected with the said base by means of more or less resilient bent conducting straps 5 and 6. The two straps 5 and 6 are connected respectively with conductors .i and l which are positioned in recesses in'the back of the base and which project respectively at the bottom and top thereof. These conductors may be connected directly to the bus bars of a. panel board or they may be provided with suitable terminals to which conducting wires may be attached. Referring particularly to Fig. 3 it will be observed that the strap 6 and the conductor 8 are connected by means of a shouldered stud 9. The strap 6 is additionally held by means of the screw Hi. It will be understood that the strap 5 at the left is similarly connected with the conductor 1.

Carried by the base I at the front thereof and Within the cover are two forward projecting metal 5 supporting plates H, H which may be advantageously held in place by means of the same screws 9 and II) which hold the contact straps 5 and 6. Carried by the said plates H, I l adjacent the front thereof is a transverse insulating bar I! which serves to hold the plates in proper spaced relationship. This bar i2 is also utilized for attaching the cover 2, a screw 13 being provided which extends through the cover and into the said bar or into a nut thereon.

Carried by the said plates I I, II and extending transversely between them is a pivot pin I 4 which is insulated from the plates by means of suitable insulating washers. Pivotally mounted on the pin I4 is a contact carrying member which preferably and as shown consists of two similar molded elements l5 and I6. These two elements are similar to each other except that they are right and left. The said elements I5 and I6 are provided respectively with hubs I! and I8 which engage the insulating washers on the pin I3, and thus serve to hold the contact member in suitable relationship to the side plates H, II. The said elements l5 and I6 of the contact member are further provided with bosses l9 and 20 which project oppositely from the main body portions of the said elements and which contact with each other in their inner faces. The said elements I 5 and [6 are still further provided with inward projecting barrier portions 2| and 22 which contact with each other at their inner faces. It will thus be apparent that when the two elements l5 and I6 are in their assembled relationship they are in engagement at the inner faces of the lugs and the barrier portions. These elements are preferably held in aligned relationship by a transverse screw or rivet at 23 and by means of a dowel pin 24, as shown in Fig. 6.

Movable electrical contacts 25 and 26 are carried by the respective elements 15 and I6, these contacts being adapted to engage and disengage the respective stationary contacts 3 and 4. Pref erably as shown in Figs. 6 and 4 the lugs l9 and 20 are provided respectively with slots 21 and 28 into which portions of the corresponding contacts 25 and 26 may fit. The contacts are removably held in place by means of screws at 23, 29. The two contacts 25 and 26 are connected together by a bi-metallic U-shaped thermostatic strip 30, which strip may be riveted to tail pieces formed on the respective contact elements, as clearly shown in Fig. 4. The strip 30 is provided with a projection or lug 3|, which enables the strip to serve as a latch.

It will be observed that the elements l5 and I6 as shown and described are well adapted to be molded, the two elements contacting directly with each other and constituting the entire insulating portion of the contact member. This is in contrast with the constructions shown in my aforesaid patents in which the contact member included spaced side plates with separate transverse members between them for maintaining them in spaced relationship and for holding the movable contacts.

A suitable spring is provided for biasing the contact member and the contacts thereon toward the open-circuit position. Preferably and as shown this is a coil spring 32 surrounding one of the bosses H or it.

There is provided a movable member 33 which I will term an actuator or actuating member, this member serving as the means for moving or actuating the contact member for normal switching purposes. or to effect closing of the circuit after automatic opening thereof. The actuator 33 is pivotally mounted on the pivot pin ll between the two elements l5 and ii of the contact member. The actuator is shown as being made of sheet metal bent to form two side members connected by integral cross members. The side members are apertured to receive the said pivot pin I4 and the said side members carry between them a transverse pin or roller 34. At normal temperatures the lug 3| on the thermostatic latch 33 engages the roller 34, and thus the said latch serves to mechanically connect the actuator with the contact member so that the two may move in unison.

For manually operating the actuator 33 I provide a handle member 35 which projects forward through an opening in the cover 2 and which is preferably mounted on a pin 36 extending transversely between the two side plates II, II. The pin 36 is insulated from the side plates'by means of suitable washers. Spacing bushings 31 are provided for holding the handle member 35 in central position and a spring 38 surrounds one of these bushings and serves to bias the handle toward its open-circuit position. The handle member 35 is connected with the actuator 33 by means of two similar links 33, 33, the links being pivoted to the handle member at 46 and to the actuator at H.

When the parts are in the relative positions shown in Fig. 4 the links 39 cooperate with the handle member itself to form a toggle action which looks the parts in position with the movable contacts 25 and 26 pressed into firm engagement with the stationary contacts 3 and 4. Continued movement of the handle in the clockwise direction is prevented by the engagement of an extension 42 thereon with the pivot pin ll. The pivotal axis at 40 is at the left of a straight line connecting the pivotal axes at 36 and II and thus the handle member and the links 39 serve to resist the tendency of. the contact member to move in the clockwise direction under the influence of the spring 32 and of the resilient straps 5 and 6 supporting the contacts 3 and 4. At the same time the toggle action holds the handle member in its upper closed-circuit position, resisting the tendency of the spring 33 to move it in the counterclockwise direction.

The above described toggle action can be released by pressing the handle toward the left, the parts then moving under the action of the springs 32 and 38 to the relative positions shown in Fig. 3. The movable contacts 25 and 26 are thus disengaged from the stationary contacts 3 and I and the circuit is broken at two separate places. By moving the handle toward the right the several parts can be restored to their relative positions as shown in Fig. 4 and the circuit can be reestablished.

As already explained, the bi-metallic strip 30 is electrically connected between the movable contacts 25 and 26. It is adapted to be deflected outward upon the passage of excess current therethrough with the result that the lug 3| is disengaged from the roller 34, as indicated by dotand-dash lines in Fig. 4. When this occurs the contact member moves automatically to the position shown in Fig. 3, this movement not being in any way dependent upon the handle and the actuator. In fact the handle may be held in the position shown in Fig. 4 without in any way interfering with the automatic releasing action. It will be understood however that, as already explained, the handle is ordinarily held in its ing elements I! and I6.

closed-circuit position by reason of pressure transmitted through the links 39. As soon as the thermal strip is released from its engagement with the actuator, this pressure through the links 39 is instantly released, and the handle member and the actuator immediately move to their open-circuit positions whereupon the lug 3| is again engaged with the roller 34 as shown in Fig. 3.- Movement of the handle member and actuator to their open-circuit positions occurs substantially simultaneously with the movement of the contact member. The parts can'be restored to their closed-circuit positions as shown in Fig. 4 by merely moving the handle upward.

As already pointed out there are insulating walls adjacent four sides of the path of move ment of each movable contact, thus substantially completely surrounding the said path. One of the said walls consists of the outer surface or wall of the corresponding contact carrying element, as for instance the wall 43 on the element l6. Another wall is an arcuate wall such as u on a laterally projecting cheek piece formed integrally with the corresponding element I! or IE as shown in Figs. 3 and 6. The third wall consists of the adjacent inner surface or wall 45 of the cover 2, as shown in Fig. 5, and the fourth wall consists of the arcuate surface or wall Ii formed on a forward projection at the front of the base I. Thus there are two movable walls 43 and 44 and two stationary walls 45 and 46 which cooperate to substantially completely enclose the path of movement of the movable contact. These walls serve to conflne-arc-formed gases and to prevent such gases from having free access to the other parts of the circuit breaker.

From an inspection of Figs. 3, 4 and 5 it will be evident that the electro-responsive strip 30 is between and closely adjacent the rupture positions of the contacts of the respective pairs. However, the movable walls of the contact member at l3, l3 effectively shield the said strip from the effects of any arcing that may occur between the contacts.

Reference has already been made to the barrier portions 2| and 22 formed on the contact carry- These two portions cooperate to form a barrier which is positioned between the side elements of the contact member and which extends circumferentially for a sufiicient distance to cover and protect the termostatic strip substantially from one end to the other thereof. This barrier not only serves to mechanically protect the thermostatic strip during assembly of the circuit breake. parts, but it also serves in cooperation with the side portions of the contact carrying elements and in cooperation with the before-mentioned enclosing walls to prevent arc-formed gases from having access to the said strip.

From an inspection of Figs. 3 and 6 it will be apparent that when the cover 2 is removed the two movable contacts and 2G and also the thermostatic strip which connects them can be readily detached from other parts of the circuit breaker by merely loosening the two screws 29, 2!. The two contacts together with the saidconnecting strip constitute a detachable and replaceable unit, which unit is separately illustrated as a part of Fig. 6. It will be observed that in the embodiment of the invention illustrated the two contacts forming a part of the unit are in register with each other transversely of the direction of normal movement. In the event of injury or damage to the movable contacts or to the strip one unit for another.

this unit can be taken out or replaced as desired. It is also possible to change the-electrical characteristics of the circuit breaker by'substituting It will be understood that different alternative units may be provided, with the thermal strips 30 thereof difierently formed so as to provide diflerent electrical capacities or other desired electrical characteristics.

What I claim is:

1. The combination in an automatic circuit breaker, of a stationary contact, a movable contact adapted to engage and disengage the stationary contact, the last said contact being biased for movement inthe circuit-opening direction and being normally held mechanically against such movement, an electroresponsive element arranged to be energized upon the attainment of an abnormal current condition in the circuit so as to mechanically release the said movable contact and thus permit it to automatically move to open-circuit position, and insulating means associated with the contacts and comprising walls closely adjacent and substantially completely surrounding the path of movement of the movable contact so as to substantially completely separate and insulate the arcing zone from all parts of the circuit breaker other than the said contacts.

2. The combination in an automatic circuit breaker, of a stationary contact, a movable contact adapted to engage anddisengage the stationary contact, the last said contact being biased for movement in the circuit-opening direction and being normally held mechanically against such movement, an electro-responsive element arranged to be energized upon the attainment of an abnormal-current condition in the circuit so as to mechanically release the said movable contact and thus permit it to automatically move to open-circuit position, insulating means associated with the contacts and comprising walls closely adjacent three sides of the path of movement of the movable contact, and an insulating wall movable with the movable contact adjacent the path of movement at the fourth side thereof.

3. The combination in an automatic circuit breaker, of a stationary contact, a movable contact adapted to engage and disengage the stationary contact, the last said contact being biased for movement in the circuit-opening direction and being normally held mechanically against such movement, an electro-responsive element bodily movable with the movable contact and arranged to be energized upon the attainment of an abnormal current conditionin the circuit so as to mechanically release the said movable contactand thus permit it to automatically move to open-circuit position, and insulating means associated with the contacts and comprising walls closely adjacent and substantially completely surrounding the path of movement of the movtacts and thus permit them to automatically move to open-circuit positions, and insulating means associated with the contacts and comprising walls closely adjacent and substantially completely surrounding the path of movement of each movable contact.

5. The combination in an automatic circuit breaker, of two stationary contacts, a movable actuator, two movable contacts adapted to engage and disengage the respective stationary contacts and biased for movement in the circuit-opening direction, a thermally responsive bi-metallic strip bodily movable with the movable contacts and electrically connected between them, the said strip normally serving as a latch to mechanically connect the movable contacts with the actuator and the said strip upon being heated by an abnormal current therein serving to mechanically release the said contacts and thus permit them to automatically move to open-circuit position, and insulating means associated with the contacts and comprising walls closely adjacent and substantially completely surrounding the path movement of each movable contact.

6. In an automatic circuit breaker, the combination of a stationary contact, a pivotally movable contact adapted to engage and disengage the stationary contact and normally held mechanically in its engaged position, an electroresponsive element arranged to be energized upon the attainment of an abnormal current condition in the circuit so as to mechanically release the movable contact and thus permit it to automatically move to disengage the stationary contact, and insulating means associated with the contacts and comprising convex and concave walls closely adjacent the path of pivotal movement of the movable contact and respectively positioned inward and outward therefrom.

7. In an automatic circuit breaker, the combination of two stationary contacts, a contact carrying member pivoted for movement about a transverse axis and having two contacts adapted to engage and disengage the respective stationary contacts, electro-responsive means normally holding the contact member with its contacts in the contact engaging position and arranged to be energized upon the attainment of an abnormal current condition in the circuit so as to release the said contact member and permit it with its contacts to automatically move in the contact disengaging direction, and insulating means associated with the contacts and comprising two pairs of convex and concave walls closely adjacent the paths of pivotal movement of the respective movable contacts.

8. In an automatic circuit breaker, the combination of two stationary contacts, a contact carrying member pivoted for movement about a transverse axis and having two contacts projecting transversely therefrom in opposite directions and adapted to engage and disengage the respective stationary contacts, electro-responsive means normally holding the contact member with its contacts in the contact engaging position and arranged to be energized upon the attainment of an abnormal current condition in the circuit so as to release the said contact member and permit it with its contacts to automatically move in the contact disengaging direction, and insulating means associated with the contacts and comprising two pairs of convex and concave walls closely adjacent the paths of pivotal movement of the respective movable contacts.

9. An automatic circuit breaker comprising in combination, a stationary contact, a pivotally movable contact adapted to engage and disengage the stationary contact and normally held mechanically in its engaged position, an electro- 5 responsive element arranged to be energized upon the attainment of an abnormal current condition in the circuit so as to mechanically release the movable contact and thus permit it to automatically move to disengage the stationary contact, and insulating means associated with the contacts and comprising a movable convex wall and a stationary concave wall both closely adjacent the path of pivotal movement of the movable contact and respectively positioned inward 5 and outward therefrom.

10. An automatic circuit breaker comprising in combination, a stationary contact, a movable contact adapted to engage and disengage the stationary contact, the last said contact being biased for movement in the circuit-opening direction and being normally held mechanically against such movement, an electro-responsive element arranged to be energized upon the attainment of an abnormal current condition in the circuit so as to mechanically release the said contact and thus permit it to automatically move to open-circuit position, two insulating walls movable with the movable contact closely adjacent two sides of the path of movement thereof, and stationary insulating means associated with the contacts and comprising two walls closely adjacent the remaining two sides of the path of movement of the movable contact.

11. An automatic circuit breaker comprising in combination, two stationary contacts, two movable electrically connected contacts adapted to engage and disengage the respective stationary contacts, the last said contacts being biased for movement in the circuit-opening direction and being normally held mechanically against such movement, an electro-responsive element bodily movable with the movable contacts and electrically connected between them to be energized upon the attainment of an abnormal current condition in the circuit and serving when so energized to mechanically release the said contacts and thus permit them to automatically move to opencircuit positions, two pairs of insulating walls movable with the respective movable contacts closely adjacent two sides of the respective paths of movement thereof, and stationary insulating means associated with the contacts and comprising two pairs of walls closely adjacent the remaining two sides of the respective paths of movement of the movable contacts.

12. An automatic circuit breaker comprising in combination, two stationary contacts, a contact carrying member pivoted for movement about atransverse axis and having two contacts projecting transversely therefrom in opposite directions and adapted to engage and disengage the respective stationary contacts, electro-responsive means normally holding the contact member with its contacts in the contact engaging position and arranged to be energized upon the attainmentof. an abnormal current condition in the circuit so as to release the said contact member and permit it with its contacts to automatically move in the contact disengaging direction, and trans- 7 versely projecting cheek pieces on the respective side elements of the contact member having convex surfaces substantially concentric with'the pivotal axis and adjacent the pathsof movement of the respective movable contacts.

13. The combination in an automatic circuit breaker oi astationary contact, a movable contact'adapted to'engage and disengage the stationary contact, the last said contact being biased for movement in the circuit-opening direction and being normally held mechanically against such movement, an electro-responsive element closely adjacent the rupturing position of the contacts and bodily movable with the movable contact, the said electro-responsive means being arranged to be energized upon the attainment of an abnormal current condition in the circuit so as to mechanically release the said contact and thus permit it to automatically move to opencircuit position, and insulating means associated with the contacts and comprising walls closely adjacent and substantially completely surrounding the path of movement of the movable contact, one of the said walls being movable and being positioned between the rupturing position of the contacts and the said electro-responsive means so as to serve as a shield for the latter.

14. The combination in an automatic circuit breaker, of two stationary contacts, two movable electrically connected contacts adapted to engage and disengage the respective stationary contacts, the last said contacts being biased for movement in the circuit-opening direction and being normally held mechanically against such movement, an electro-responsive element between and closely adjacent the rupturing positions of the respective contacts and bodily movable with the movable contacts, the said electro-responsive means being electrically connected between the movable contacts to be energized upon the attainment of an abnormal current condition in the circuit and serving when so energized to memovable actuator, a movable contact member comprising two spaced insulating side elements and two electric contacts adapted to engage and disengage the respective stationary contacts, the said contact member being biased in the circuitopening direction, an electro-responsive means on the contact member positioned between the side elements and electrically connected between the movable contacts, the said means normally serving to mechanically connect the said contact member with the actuator and being automatically releasable upon the passage or excess current to' permit independent circuit-opening movement of the contact member, and a barrier on the contact member between the side elements thereof and at the outside of the electro-responsive means which barrier extends substantially from one end of the electro-responsive means to the other.-

16. In an automatic circuit breaker, the combination of two stationary electric contacts, a movable actuating member, a movable contact member comprising two spaced insulating side elements and two electric contacts adapted to engage and e the respective stationary I ed for use as a part of an automatic circuit breakcontacts, the said contact member being mov-' able about a transverse axis and biased in the circuit-opening direction, a bi-metallic thermal strip on the contact member positioned between the side elements and electrically connected in series between the movable contacts, the said strip normally serving asa latch to mechanically connect the said contact member with the actuating member and being automatically releasable upon the passage of excess current to permit independent circuit-opening movement of the contact member, and a barrier on the contact member between the side elements thereof and outside of the thermal strip which barrier extends circumferentially substantially from one end of the strip to the other.

17. An automatic circuit breaker comprising in engage and disengage the respective stationary contacts, and a bi-metallic thermal strip on the contact member positioned between the side elements and radially inward from the barrier, the

said thermal strip being electrically connected in series between the movable contacts and serving upon the passage of excess current to mechanically release the iZ-imtact member from the actuating member to permit independent circuitopening movement of the contact member.

18. An automatic circuit breaker comprising in combination, two stationary electric contacts, a movable actuating member, a contact carrying member movable about a transverse axis and comprising two spaced insulating side elements each formed with a transversely projecting integral boss having a transverse notch therein, the said contact member being biased in the circuitopening direction and being normally mechanically connected with the actuating member, two electric contacts fitting the notches in the respective side elements and adapted to engage and disengage the respective stationary contacts, and a bi-metallic thermal strip on the contact member between the side elements and electrically connected in series between the movable contacts, the said thermal strip serving upon the passage of excess current to mechanically release the contact member from the actuating member to permit independent circuit-opening movement of the contact member.

19. A detachable and replaceable unit adapted for use as a part of an automatic circuit breaker and comprising in combination, two circuit breaker contacts adapted to directly engage respectively with two other circuit breaker contacts, and a bi-metallic thermal strip connected with the first said contacts to constitute an electrical connection between them and adapted to control the automatic operation of the circuit breaker.

20. A detachable and replaceable unit adapter and comprising in combination, two movable circuit breaker contacts positioned in register with each other transversely of the direction of movement and adapted to directly engage respectively with two stationary circuit breaker contacts, and a bi-metallic thermal strip connected with the first said contacts to constitute an electrical connection between them and adapted to control the automatic operation of the circuit breaker.

21. A detachable and replaceable unit adapted for use as a part of an automatic circuit breaker and comprising in combination, two similar closely adjacent circuit breaker contacts adapted to directly engage respectively with two other circuit breaker contacts, and a U-shaped bi-metallic thermal strip connected with the first said contacts to constitute an electrical connection between them and adapted to control the automatic operation of the circuit breaker.

22. A detachable and replaceable unit adapted for use as a part of an automatic circuit breaker and comprising in-combination, two similar closely adjacent transversely registering circuit breaker contacts adapted to directly engage respectively with two other circuit breaker contacts, and a U-shaped bi-metallic thermal strip connected with the first said contacts to constitute an electrical connection between them and adapted to control the automatic operation of the circuit breaker.

23. The combination in an automatic circuit A breaker, of a detachable unit comprising a set of two contacts and a bi-metallic thermal strip connected with the two contacts to constitute an electrical connection between them, another set of two contacts, a movable member on which one of the said sets of contacts is carried so as to be brought into or out of engagement with the contacts of the other set, the said member being biased for movementtoward its open-circuit position, and means mechanically cooperating with the said thermal strip to normally prevent movement of the contact carrying member to its opencircuit position, the said bi-metallic strip by reason of its mechanical cooperation with the last said means and its electrical connection between the contacts of one set serving to mechanically release the contact carrying member and permit it to automatically move to open-circuit position upon the attainment of an abnormal current condition in the circuit.

24. The combination in an automatic circuit breaker, of two stationary contacts, a movable contact carrying member biased for movement toward its open-circuit position and normally mechanically held against such movement, and a unit detachably mounted on the contact carrying member and comprising two movable transverseiyregistering contacts adapted to directly engage respectively with the said stationary contacts and a bi-metallic thermal strip connected with the movable contacts to constitute an electrical connection between them, the said bi-metallic strip being heated upon the attainment of an abnormal current condition in the circuit and being thus deflected so as to mechanically release the contact member and permit it to automatically move to open-circuit position.

25. The combination in an automatic circuit breaker, of two stationary contacts, a movable contact carrying member biased for movement toward its open-circuit position, a separate unit detachably mounted on the contact carrying member and comprising two movable contacts adapted to directly engage respectively with the said stationary contacts and a bi-metallic thermal strip connected with the movable contacts to constitute an electrical connection between them and formed to serve in and of itself as a releasable latch, and means adapted to be releasably engaged by the said strip or latch to normally prevent movement of the contact carrying member to its open-circuit position, the said bimetallic strip or latch by reason of its releasable mechanical engagement with the last said means and its electrical connection between the contacts of one set serving to mechanically release the contact carrying member and permit it to automatically move to open-circuit position upon the attainment of an abnormal current condition in the circuit.

JOSEPH SACHS. 

